An informative, sequence on the making of these Skulls can viewed on this journal.

This life size, anatomically correct, lead
crystal skull was first meticulously hand crafted in soft modeling
wax.
Employing the lost wax casting process it was encased in a plaster investment
which had the wax steamed out leaving a cavity in the form of the original wax.
The now hollow mould, with sufficient glass, is placed into the electric, computer
controlled kiln.

Fired to approximately 850
degrees centigrade, melts the lead crystal into the
mould. A full week is required to gradually cool and anneal
the glass, removing stress, before the encasement is carefully
broken away revealing the kiln cast skull.
To achieve the fine, detailed finish requires many patient hours hand working
and polishing the entire surface.